Fault Isolation Procedures; General Troubleshooting - Zenith ZVM-131 Service Manual

Table 1
General Troubleshooting
PROBLEM
POSSIBLE CAUSE
Dead monitor
No power at source
Power cord
Fuse
Connector 3R8
Connector 3S8
Power switch
No display
RGBcable
95 volt supply
No color
GREENIWHITE switch
Software produces monoc-
hrome display
Green color only
GREENIWHITE switch
Software produces green dis-
play
Out of focus
Focus control
Raster displayed G2 control
Display does not
fit
P1, P2 on the sweep board
on CRT
Width control
95 volt adjustment
Fault Isolation Procedures
Have the monitor sync-locked to a signal, if possible, be-
fore starting this procedure.
Always reference the DVM or oscilloscope to DC (cold)
ground unless instructed otherwise.
A 10X probe is recommended for use with the oscillo-
scope.
1. With a DVM, measure the voltage at pin 2 of con-
nector 3V3 on the main board (see Figure 16).
If
+
150 VDC is present, proceed to step 2.
If
+
150 VDC is not present, replace the main board.
Page 20
2.
3.
4.
With a DVM, measure the voltage at pin 2 of con-
nector 3F3 on the main board.
If the voltage is from
+
4.5 VDC to
+
12 VDC, pro-
ceed to step 3.
If the voltage is less than
+
4.5 VDC, replace the
main board.
With a DVM, measure the voltage at pin 2 of con-
nector 303 on the main board.
If the voltage is from
+
12 VDC to
+
26 VDC, pro-
ceed to step 4.
If the voltage is more than
+
26 volts, replace the
main board.
With a DVM, measure the voltage at pin 2 of con-
nector 3G3 on the main board. A value of
+
0.3 VDC
should be observed. Observe this point with an oscil-
loscope and verify the presence of horizontal drive
pulses.
If the pulses are present, proceed to step 5.
If the pulses are not present, replace the main board.
5. With an oscilloscope, measure the supply voltages at
connector 303 on the main board. The voltages
should be:
Pin 1 170 volts peak to peak
Pin 2
+
26 volts DC
Pin 3 Ground
Pin 5 60 volts peak to peak
Pin 6 140 volts peak to peak
If all voltages are correct, proceed to step 6.
If any voltage is not correct, replace the sweep as-
sembly.
6. Use a high voltage probe to verify the presence of
26 kV on the CRT anode lead.
If
+
26 kV is present, proceed to step 7.
If
+
26 kV is not present, replace the sweep assem-
bly.
Servicing